A Research And Design Of Compact Planar MIMO Antenna

With the development of communication technology,the technology of Multiple-Input-Multiple-Output(MIMO),which can effectively suppress multipath fading,improve system capacity and increase system stability,has quickly become one of the key technologies of the fourth and fifth generation mobile communication.MIMO antenna is the RF transmitter of MIMO communication system,miniaturization,multiband and decoupling technologies are important research fields.Recently,MIMO antennas tend to be miniaturized.How to design an antenna with sufficient isolation under the condition of limited space size is the difficulty and key of MIMO antenna design.At present,the research on MIMO antenna miniaturization is usually carried out from the perspective of single antenna unit miniaturization.Large spacing between antenna units is still required in many of the designs,which limits the overall size.In this paper,the miniaturized MIMO antenna is designed by reducing the unit spacing.The traditional design procedure of MIMO antenna is to design a single antenna first and then the decoupling structure is added.However,the additional decoupling structure often breaks the original antenna match.As a result,impedance rematch needs to be conducted and often requires repeated debugging.In this paper,based on another design method,a network with port isolation characteristics is firstly proposed,and then part of the network is converted into a radiation structure.Based on the above two viewpoints,this paper explores miniaturization and decoupling of the multiband MIMO antenna respectively,and the main works are completed as follows:1.The traditional miniaturization technology of MIMO antenna is summarized.From the aspect of reducing the spacing between element antennas,a dual band MIMO antenna with close placement and tight coupling is designed.The spacing is only 10 mm(0.083λ).The mutual coupling of antennas in the desired frequency band is eliminated by introducing the modified stubs and novel slots.The isolation requirement is satisfied and miniaturization is realized.After manufacture and testing,it is proved that the MIMO antenna works in a range of 2.15GHz-2.64 GHz and 3.36GHz-3.53 GHz,covering the WLAN and WiMAX bands.The Envelope Correlation Coefficient(ECC)is less than 0.2 in both of the working bands.2.Based on the traditional filter network structures,a band-resistance filter with three stop bands is designed by using the stepped impedance resonator and parallel coupled micro-strip line as resonant units.The central frequencies of the three stop bands can be flexibly independently controlled by adjusting the impedance ratio and other parameters.3.Using the proposed band-stop filtering network as a prototype,the port isolation of MIMO antenna is realized by using two of the stop bands.By transforming part of the network structure into the PIFA-like monopole radiation structure,a dual-frequency MIMO antenna is finally realized.The isolation degree near the center operating frequency reaches more than 20 dB.The antenna is simulated and fabricated,which can works in a range of 2.35GHz-2.52 GHz and 5.65GHz-6.1GHz,covering the WLAN band.The ECC is less than 0.2 in the working bands.